66 POPULAR SCIENCE MONTHLY. 



It would be clear that the change was due to the substitution of 

 families of 0, 1, 2 and to a slight extent of ?>, for fifty per cent, of 

 the families over 3, that all these groups of larger families had given 

 up the same proportion to swell the groups of small families. This 

 would point clearly toward restriction as a cause. 



Suppose that the following were the facts: 



Children 0123456789 10 11 12 



1803-1814 2 4 8 10 16 20 16 10 8 4 2 

 1865-1874 6 8 10 16 20 16 10 8 4 2 



In this case it is clear that the change was due to^the substitution 

 throughout of families less in each case by three children. There is 

 no cutting off equally from all the higher groups. Families of 4 and 

 5 for instance increase in number. There is no special increase of 

 the 0, 1, 2 families. The movement has been simply a general de- 

 crease in size, a moving backward of the general tendency to produce. 

 Such an appearance in the statistics would point toward decreased 

 reproductive capacity. 



In our second illustration there would probably be in connection 

 with the lowered average tendency a reduction of the variability. That 

 is the range or spread from the common occurrence (a four-children 

 family) would be less, and our figures would be something like the 



Generalizing the argument we may say : 



In so far as conscious restriction is the cause of the lesser fertility 

 of the late decades it will show itself by a disturbance of the form of 

 distribution of the different-sized families. 



1. Kestriction as commonly considered would increase the 0, 1 

 and 2 and to some extent 3 children families at the expense of all 

 larger families. For according to the comuion view there would be 

 no influence of restriction in a family which had already five or six 

 children. 



2. Fach group of large-sized families would then lose in proportion 

 to the number of families in it, the psychological and social sources of 

 the custom being in no way correlated with fertility. 



3. The result will be the appearance in the statistics of late decades 

 of two species of families, one showing the natural tendency and in 

 every way comparable to the species shown in the first decades, the 



